1. Field of the Invention
The present invention refers to a device for simultaneously measuring fluorescent light emitted by sample-reagent mixtures contained in a plurality of reaction vessels.
The invention further concerns an apparatus wherein such a device is used.
In order to measure fluorescent light emitted by sample-reagent mixtures contained in a plurality of reaction vessels simultaneously, it is necessary to convey fluorescent light beams emitted from all the reaction vessels in parallel to a corresponding plurality of light receivers, e.g. by means of a corresponding number of optic fibers. The output signals of the latter have to be processed by suitable electronic signal processing circuits in order to obtain the desired information from the fluorescent light detected with the light receivers.
Since intensity of fluorescent light to be measured is very low, it is mandatory that the detection system as a whole operates at a level of noise which is as low as possible.
An additional requirement is that the number of light receivers should be as small as possible in order to reduce the cost of the electronic and signal processing means and in order to increase read out speed.
A further requirement is that the price of the light receiver means is very low
2. Description of the Prior Art
Known prior art are unable to provide a solution which satisfies all of the above-mentioned requirements. Prior art use of charge coupled devices (CCDs) as light receivers makes it possible to operate at a relatively low level of noise, but CCDs are rather expensive if only a small number of pixels is required. Due to the high number of pixels of a CCD for fast read out, a CCD requires expensive electronic signal processing means. Use of a CCD becomes even more expensive if an integrated pixel binning function (reading of signals provided by a group of pixels) is used.
Another disadvantage of a CCD is that its quantum efficiency is low. This disadvantage can be diminished by use of a more expensive back-illuminated CCD or by adding an image intensifier in front of the CCD. This latter approach is not only very expensive, but in addition reduces the quantum efficiency.
Further disadvantages of a CCD are that, in general it has a poor dynamic range, and it only enables destructive reading of a pixel because the signal reading erases the signal being read (reset).
Another possible approach is the use of photomultiplier tube arrays (PMT-arrays) as light receiver means, but this type of arrays have a high level of cross-talk, are of relatively large size, and the additional external means necessary to reduce noise to an acceptable level are rather expensive.
Another possibility would be to use an array of discrete photodiodes as light receivers. This would be a cheap solution, but their high noise and/or high dark current makes such photodiodes wholly unsuitable for the measurement of fluorescent light within the context of the instant invention.